The present invention relates to a linear beam irradiator for irradiating the surface of an original sheet in the main scanning direction on an optical image reader, for example.
A conventional linear beam irradiator is explained by taking an optical image reader as example for the sake of convenience.
In recent years, an optical image reader came to be widely used as for a reading unit for a facsimile, scanner, barcode reader, etc., and LED array realized by disposing LED chips in linear shape is used as original irradiating means of this kind of equipment.
FIG. 14 shows a structural drawing of a conventional optical image reader. In FIG. 14, the original sheet 51 (hereinafter referred to xe2x80x9coriginal 51xe2x80x9d) is irradiated by a LED array 52 used as original irradiating means, and the light reflected on this original 51 is converged by a rod lens array 53, and input in a photoelectric converting element array 54, to be converted into an electric signal.
Here, the distance from the photoelectric converting element array 54 to the original 51 is usually 10 mm or so, and the respective rod lenses constituting the rod lens array 53 have a columnar shape of 0.6 xcfx86mm or so.
FIG. 15 indicates the construction of a conventional LED array, which is constructed by arranging a plural number of LED chips 62 linearly on a printed circuit board 61 forming the conductive layer of a circuit. Usually, 24 to 32 pieces of LED chip 62 are disposed on one printed circuit board. One piece of LED chip 62 has a length of about 2 mm, and the respective LED chips 62 are arranged at intervals of 5 mm or so.
Moreover, the Japanese patent laid-open publication No. 6-180009 discloses an original irradiating means of a construction realized by disposing a light source at both ends or at an end of a light conductor, to transmit the light from the light source through said light conductor. With this construction, it becomes possible to form a light diffusing area such as chopping wave surface, for example, on one side face in the longitudinal direction of the light conductor, so as to irradiate a concentrated linear beam from the other side face in the longitudinal direction.
By the way, while a original irradiating means works all right if only a linear light beam is obtained in the scanning direction, said construction using LED array has a defect of lowering the irradiation efficiency because the LED chips 62 also diffuse light in the subscanning direction respectively. Moreover, since the LED chips are provided at prescribed intervals, this not only produces deviation of illuminance on the surface of the original, requiring processing such as correction of shading, etc. but also deteriorates the image reading performance of the image reader itself even with such processing. Furthermore, in order to keep the deviations of illuminance on the surface of the original to a minimum, it is necessary to keep a certain distance between the original 51 and the LED array 52, which would require a larger number of LED chips, expand the size of the unit itself and increase cost.
In addition, this interface of the chopping wave which is disclosed in the Japanese patent laid-open publication No. 6-180009 is covered with air of an index of refraction lower than that of the light conductor. Therefore, the light irradiated on said interface of the chopping wave among the light transmitting through the light conductor is totally reflected inside the light conductor to eventually go out from the other side face. However, since the entire light doesn""t necesarily reflect back to the inside of the light conductor so a portion of light leaks to outside the light conductor, deteriorating the transmission efficiency.
The object of the present invention is to provide a linear beam irradiator capable of controlling deviation of illuminance on the surface of the original, without reducing the irradiation efficiency of the LED array. Another object is to provide a small-sized linear beam irradiator with shortened distance between the light irradiating surface and the original. Still another object is to provide a linear beam irradiator capable of drastically improving the transmission efficiency of light and sharply reducing the number of LED chips. Yet another object is to provide a low-cost linear beam irradiator.
To achieve said objects, the present invention adopts the following means: First, the present invention presupposes a linear beam irradiator comprising a light conductor 1 having light permeability, a light refraction and reflection area 2 provided on one side face in the longitudinal direction of said light conductor 1 and a light source on the surface at both ends of said light conductor 1. By this construction, the light emitted from said light source gets into the light conductor 1, is refracted or reflected in said light refraction and reflection area 2, and goes out in the form of linear beam from the other side face in the longitudinal direction opposing said light refraction and reflection area 2.
In said linear beam irradiator, the present invention is constructed by comprising said light refraction and reflection area 2 composed of a large number of interface of the chopping wave, and a diffusing surface 8 provided in a way to cover the light refraction and reflection area 2. By this construction, the light which entered in the parts other than said light refraction and reflection area 2 of the light conductor 1, is transmitted through the light conductor 1 while repeating total reflection on the inner face of this light conductor 1, to eventually enter the light refraction and reflection area 2 and go out in the form of linear beam from the outgoing surface. At that time, since the light refraction and reflection area 2 is composed of a large number of interfaces of chopping wave, the light which entered the light refraction and reflection area 2 is reflected downward and goes out from the outgoing surface, thus going out efficiently. Moreover, even in the case where the light which entered said light refraction and reflection area 2 is transmitted through this light refraction and reflection area 2, it is reflected back to the inside of the light conductor 1 by the diffusing surface 8 formed on the light refraction and reflection area 2, and can form a linear beam efficiently.
If said diffusing surface 8 is disposed across a space (air layer, for example) not optically matching with said light refraction and reflection area 2, the amount of light directly entering said diffusing surface 8 decreases and the efficiency improves.
The shape of said light conductor 1 is decided in such a way that the sectional area gradually diminishes from both ends toward the center. In this case, a light source is disposed at both ends of said light conductor 1. Moreover, the shape of said light conductor 1 may also be decided in such a way that the sectional area gradually diminishes from one end toward the other. In that case, a light source will be disposed at an end of said light conductor 1, and a light terminal 38 will be provided at the other end as construction.
The other side face in the longitudinal direction irradiating the light of said light conductor 1 must be a plane perpendicular to both end faces of said light conductor 1. Thus the surface irradiated with light such as original paralles the other side face (light irradiating surface).
The sectional shape of said light conductor 1 can be circular, elliptical, etc. In the case where a light conductor 1 with an elliptical sectional shape is used, the light refraction and reflection area 2 is preferably disposed on the focal point on one side of the ellipsis. Moreover, said light conductor 1 may also have a sectional shape formed by combining 2 circles of different diameters. In that case, the circle with larger diameter will be furnished with the light transmitting function, while the circle with smaller diameter will have the light irradiating function.
To efficiently conduct the light emitted from said light source to the light conductor 1, a connecting part 6 is provided between the light source and the light conductor 1. Here, the connecting part 6 shall preferably be arranged in such a way that the incident light from the light source at both ends of the light conductor 1 has a length in longitudinal direction and a diameter satisfying the conditions of total reflection at the inner face of the light conductor 1.
In the case where the sectional area is made to gradually diminish from one end toward the other, a light terminal 38 for treating the light which reached the other end is disposed. This light terminal 38 will be constructed by comprising, at the outer circumference and the end face, a light shielding layer for shielding the light from outside or a light diffusing layer for diffusing light or a light reflecting layer for reflecting light.
Said light source, formed on a concave reflecting face 5, will be constructed by disposing a light emitting diode on a printed circuit board. Said light emitting diode and said connecting part 6 will be made of transparent resin having one same index of refraction as said light conductor 1, and said light emitting diode or said light conductor 1 will be connected in a way to optically match with each other.